Though less visible than their publicly traded counterparts, private companies have plenty of clout in the U.S. economy. This year the 339 companies on our roster of closely held businesses sold a trillion dollars' worth of goods and services and employed4 million people. Last year's count of privately held U.S.businesses with at least $1 billion in revenue was only 305.

Apart from a little inflation, which could tip a borderline sales figure over the minimum, a growth factor for our list is the recent and immense popularity of private equity investing. The private equity players buy divisions or entire companies, fix them and run them, either flipping the properties or, in some cases, holding on to them for several years. Thus did SunGard Data Systems (number 55) and Metro-Goldwyn-Mayer (number 180) join this list in the last 12 months. By going private, a company can wash its hands of the paperwork-heavy Sarbanes-Oxley law.

We define as "private" a company that either has too few shareholders to be required to file public financial statements or restricts its share ownership to a limited group, like employees. Some on our list have closely held stock but file financials with the Securities & Exchange Commission because of publicly traded debt. Example: Solo Cup.

We leave out companies that do not pay taxes (like Mohegan Sun Casino), real estate investment and management companies, cooperatives, mutuals, auto dealerships, companies with fewer than 100 employees and companies 50% or more owned by other private, public or foreign companies.

For businesses with both public and private subsidiaries, we count only those revenues attributable to the private operation. For example, our $66.7 billion sales figure for Cargill, which is ranked first on our list, excludes the $4.4 billion in revenues of its public subsidiary, the Mosaic Co., which sells crop nutrients and animal feed.

For more information on America's largest private companies and a free PDA download of this year's list, go to www.forbes.com/private.

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